The present invention relates to a method for correcting phase distortions produced for every line (for every phase encode: a set of one-dimensional data measured at each step of the phase encode is called one line) in signals measured by means of a magnetic resonance imaging device and a device for realizing same.
Heretofore, as disclosed in JP-A-Sho 61-187850, with respect to the phase distortion in the detection signal, the object of correction was offset phase distortions having a constant value, remaining unchanged for different lines and phase distortions, which similarly thereto, remain unchanged for every line, but vary linearly on the image.
FIG. 1 is a scheme indicating the principle of the generation of phase distortions, which are the object of the present invention.
When the intensity of the applied gradient magnetic field is increased in order to shorten the imaging time, magnetic influences, in the form of noises due to the eddy current effect, etc., largely appear. The degree of these magnetic influences dependently varies on the intensity of the gradient magnetic field. As the result, the pulse of the read-out gradient magnetic field G.sub.x varies as indicated by an arrow 14 and corresponding thereto, the point of time, where the area thereof is equal to the area Sl of a pulse 11, varies also, as indicated by a pulse 12 or 13. As the result, the point of time at the occurrence of the peak in the resonance signal varies also as indicated by an arrow 15. For this reason, supposing that the period of time T.sub.E from the point of time of the application of an RF 90.degree. pulse to the detection of the resonance signal is constant, it is impossible to detect always the peak of the resonance signal.
As the result, the phase of the detection signal includes phase distortions varying for every line, which caused blurry picture to produce deterioration of the image quality.
Heretofore, since the intensity of the gradient magnetic field was low, the amount of variations in the read-out gradient magnetic field G.sub.x indicated by the arrow 14 was ignorable. However, when the intensity of the gradient magnetic field was increased, the amount of variations varied for every line. Therefore it was a serious problematical point to be solved that phase distortions varying for every line took place.